1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a 2D-3D switchable autostereoscopic display apparatus which is compatible with a display panel that generates polarized light and with a display panel that generates non-polarized light.
2. Description of the Related Art
Stereoscopic display apparatuses display images having binocular parallax for a left eye and for a right eye to the left and right eyes of a viewer, respectively. The viewer can see a stereoscopic 3D image by perceiving the images for the left and right eyes provided by the stereoscopic display apparatus through the retinas of different eyes. Such stereoscopic display apparatuses are roughly classified into parallax barrier type stereoscopic display apparatuses and lenticular stereoscopic display apparatuses. Generally, lenticular stereoscopic display apparatuses include a display panel for producing an image signal for a right eye and an image signal for a left eye and a lenticular means installed in front of the display panel to direct the image for a left eye and the image for a right eye in mutually different directions.
There is recent demand for a stereoscopic display apparatus capable of switching between a 2D mode and a 3D mode to selectively display either a 2D image or a 3D image according to an image signal provided. To meet this demand, various 2D/3D switchable autostereoscopic display apparatuses are under development. For example, U.S. Pat. No. 5,500,765 discloses an autostereoscopic display apparatus which switches between a 2D mode and a 3D mode by a mechanical movement of a lenticular lens sheet over a display panel. However, such a mechanical switching means is vulnerable to damage from the environment, such as through impacts, vibrations, dust, humidity, etc.
To solve this problem, U.S. Pat. No. 6,069,650 discloses an autostereoscopic display apparatus which switches between a 2D mode and a 3D mode using an electro-optical medium. FIG. 1 is a cross-sectional view of the autostereoscopic display apparatus disclosed in U.S. Pat. No. 6,069,650. Referring to FIG. 1, the conventional autostereoscopic display apparatus includes a back-light unit 81, a liquid crystal display (LCD) panel 82, and a lenticular means 83 which switches between a 2D mode and a 3D mode. The lenticular means 83 includes a lenticular lens sheet 85 on which a plurality of cylindrical lenses are arranged, a flat-surfaced plate 86 facing the lenticular lens sheet 85, an electro-optical medium 84 filling the space between the lenticular lens sheet 85 and the flat-surfaced plate 86, and electrodes 88 and 87 respectively formed on inner sides of the lenticular lens sheet 85 and the flat-surfaced plate 86. According to this structure, when no voltages are applied to the two electrodes 88 and 87, the stereoscopic display apparatus operates in a 3D mode. When voltages are applied to the two electrodes 88 and 87, the stereoscopic display apparatus operates in a 2D mode.
However, in the conventional stereoscopic display apparatus of FIG. 1, only the refractive index of the electro-optical medium 84 with respect to polarized extraordinary light is controllable. Hence, the electro-optical medium 84 can only be applied to LCD panels, not to display panels that generate non-polarized light, such as, cathode ray tubes (CRTs), plasma display panels (PDPs), organic light emitting devices (OLEDs), field emission devices (FEDs), etc.
FIGS. 2A and 2B are cross-sectional views illustrating different operations of the lenticular means 83 with respect to incident non-polarized light. Typically, non-polarized light incident upon a liquid crystal material is output as two separate rays, namely, ordinary rays and extraordinary rays, polarized perpendicular to one another. In FIGS. 2A and 2B, rays having vertical lines thereon denote ordinary rays, and rays having dots thereon denote extraordinary rays. Referring to FIG. 2A, when no electric fields exist, molecules of the electro-optical medium 84 are arranged parallel to the plate 86. The lenticular lens sheet 85 is formed of a material having the same refractive index as the electro-optical medium 84 with respect to the ordinary rays. The electro-optical medium 84 is formed of a material having a lower refractive index with respect to extraordinary rays than to ordinary rays. Thus, when no voltages are applied to the two electrodes 88 and 87, the lenticular lens sheet 85 does not serve as a lens for the ordinary rays, and thus the ordinary rays are transmitted by the lenticular means 83 without being refracted. On the other hand, the extraordinary rays are refracted by the lenticular lens sheet 85 and simultaneously directed as separate images for a left eye and a right eye to the two eyes of a viewer.
Thus, when non-polarized light is incident upon the conventional lenticular means 83 in a 3D mode, some rays of the incident non-polarized light are directed in different directions toward a viewer's eyes so that a viewer sees a different image in each eye, while the other rays are directed toward the viewer's eyes so that the viewer sees both images with each eye. As a result, proper 3D image perception is impossible. In order to prevent improper 3D image perception, a polarization plate must be installed between the display panel and the lenticular means. However, this measure reduces the brightness of the display apparatus by at least 50%.